(1) Field of the Invention
The present invention relates to keyboards including keys which provide tactile feedback to a person operating the keys. More particularly, the present invention relates to a snap-action element which provides tactile feedback. The element may be incorporated within each key of a keyboard having a plurality of keys. By way of example only, the keyboard has utility in retail outlets, airline terminals, fast-food restaurant terminals, data terminals and calculators.
(2) Description of the Prior Art
Prior art keyboards are of two basic types. One type of keyboard is an array of independent or discrete keys which are actuated to connect a circuit positioned beneath the keys. Typical uses for keyboards having discrete keys include hand held electronic calculators. The second type is a keyboard wherein a flat sheet of plastic has a legend printed thereon, the legend difining areas to be pushed to actuate keys positioned beneath the flat sheet of plastic.
In the keyboard of the type having a flat legend sheet, the legend sheet defines a plurality of points or areas on the sheet which the operator may press to actuate the key associated with the particular area or point. It is highly desirable that each key of the keyboard provide the operator of the key with tactile feedback when electrical connection is made by actuation of a key. The key which is positioned beneath the flat legend sheet provides for the connection of an electrical circuit and provides the operator of the key with tactile feedback when the electrical circuit is made.
One problem with prior art keyboards having flat legend sheets is that the keys positioned beneath the legend sheet have a complicated structure which requires many separate parts and which requires a large amount of time to assemble. The relatively large amount of time to assemble the keys is related not only to the large number of parts in the key, but also to the necessary alignment of the parts to insure proper actuation of the key. A typical keyboard includes a legend sheet which defines a plurality of points which the operator of the keyboard may push to actuate the keys located beneath the legend sheet. Typically, beneath the legend sheet is a second sheet having a plurality of small projections, the second sheet being aligned with the legend sheet to provide one projection for each legend point or area on the legend sheet. The projections face downwardly into the keyboard and provide for the actuation of an arcuately shaped discrete invertible metal dome. The keyboard includes a discrete or individual metal dome for each key. The domes are positioned on a printed circuit board which provides a first circuit which is connected to the periphery of the dome and a second circuit which is positioned beneath the center of the dome so that when the dome inverts, a connection is made between the two circuits. The individual metal domes are retained on the circuit board by adhesive tape having holes through which the upper portions of the domes protrude. The cost of such a keyboard is quite high due to the relatively high number of components, and the formidable assembly task. It should be understood that in the assembly of the prior art keyboard, the center of the domes had to be aligned precisely with the small projections in order for each key to provide for electrical connection and tactile feedback. Thus, a high level of precision is necessary in the method of assembly. Moreover, because of the numerous components, the keyboard is relatively thick and presents a cluttered appearance to the user of the keyboard. A thick keyboard requires a greater space to be provided on the surface on which the keyboard is to be mounted. Furthermore, this prior art keyboard has a tendency to register a double entry when the key is pressed. Double entry often results from misalignment of the dome with the small projections. Another reason for the double entry is that the domes of the prior art tend to oscillate or bounce when actuated thereby providing for double actuation of the key. The prior art key also tended to close without tactile feedback. Closing of the key without tactile feedback is often a result of misalignment of the small projection with respect to the dome. For example, if the small projection were positioned away from the center of the dome, the projection could actuate the key without providing the user with tactile feedback.
It should be understood that the keys are actuated by the operator pressing his finger against a point on the flat flexible legend sheet. The prior art switches had the disadvantage that the sheet had to be pressed at a point very close to the underlying projection which actuates the metal dome. With prior art keyboards, if the operator pressed his finger at a point removed from the underlying projection, not only was the desired key not actuated, but there was a significant possibility that an adjacent key would be actuated.
A second type of keyboard is of the type that includes many discrete keys. Such a keyboard is disclosed in U.S. Pat. No. 3,898,421. This patent discloses a keyboard wherein discrete keys may be pushed to invert an element comprising a spherical protuberance including an annular shoulder separated from a central portion by a flexural node to provide a double snap-action element. When the actuator is depressed by a force exerted on the central portion, the annular shoulder is moved and makes contact with a pair of fixed electrodes to make electrical contact and provide a first snap action. Thereafter, the central portion undergoes a second snap action whereby the central portion is positioned between the electrodes. It is a significant drawback of the element disclosed in this patent that the actuator undergoes two snap-actions. An operator using the key by having to press the key through two snap actions may be confused as to whether electrical contact was made once or whether electrical contact was made twice. Thus, it is undesirable to provide a central portion which is capable of inversion.
It is an object of the present invention to provide a keyboard having simplified and fewer components thereby allowing for simplified methods of assembly.
It is an object of the present invention to provide a keyboard wherein the domed actuators are not required to be aligned with actuating protrusions.
It is a further object of the present invention to provide a keyboard having keys wherein the tendency for double entry is reduced. It is another object of the present invention to reduce the possibility of the key closing without tactile feedback.
It is a further object of the present invention to provide keys which are less sensitive to the imposition of forces disposed from the center of the key. Restated, it is an object of the present invention to provide a key which may be actuated by a force imposed at an area of the legend sheet removed from the center of the actuator.
It is another object of the present invention to provide a keyboard whereby the legend sheet has a dual purpose in that the legend sheet defines actuating areas and also provides a conductive circuit.
It is a further object of the present invention to provide a keyboard having a reduced number of components thereby reducing material cost and assembly cost.